1. Field of the Invention
The present invention relates to light emitting technology and more particularly, to a LED and its fluorescent powder and organic film layer. The LED has covered thereon an organic film layer containing a fluorescent powder that has added thereto Tb (terbium) ions, Gd (gadolinium) ions, Yb (ytterbium) ions and Lu (lutetium) ions. The fluorescent powder absorbs short-wave radiation λ=440˜480 nm from an InGaN semiconductor heterostructure and then radiates light of peak wavelength λ=525˜595 nm.
2. Description of the Related Art
In the development of lighting sources, white light is a blend of all the colors in the visual spectrum, resulting in the color white.
Blue light can be added to red light and green light to produce the impression of white light. Solid lighting sources of different colors can be made using this principle. Most white color solid lighting sources in production today are based on the following techniques.
One technique uses three solid lighting sources respectively based on AlInGaP, GaN and GaP to emit red, green and blue light subject to the control of an electric current through AlInGaP, GaN and GaP, enabling the red, green and blue colors of light to be mixed by a lens into white light.
Another technique uses two solid lighting sources respectively based on GaN and GaP to emit blue and yellow green light subject to the control of an electric current through GaN and GaP, enabling the red and yellow green colors of light to be mixed into white light.
In either of the aforesaid two techniques, when one solid lighting source fails, no white light can be obtained. Further, because the forward bias at one solid lighting source is different from that at the other solid lighting source, multiple control circuits are necessary, resulting in a high cost. These drawbacks are unfavorable factors in actual application.
Nichia Chemical Corp. developed a white LED in 1996 by covering an InGaN blue LED with phosphor, thereby mixing blue light and down-converted yellow light to create white light. However, the continuity of the spectrum distribution of the white light thus created is unlike sunlight. This design of white LED is simply suitable for the purpose of simple illumination.
A fourth method for producing white light was developed by Sumitomo Electric Industries, Ltd., Japan. According to this technique, a ZnSe-based white LED is made by introducing an i-ZnMgBeSe/p-ZnMgSe double cladding structure, which includes a very thin i-ZnMgBeSe layer for suppressing electron overflow and a p-ZnMgSSe layer for efficient p-type carrier concentration.